With the Saab system, head movement during a rear-end impact is minimised by a linkage connected to a pressure plate hidden in the seat back which pushes the head restraint up and forward. Essentially, it moves into a position to stop the head from making the movement backwards that causes whiplash.
Women have a particular problem with whiplash, Viano explained, because the restraints are often too far from the back of their heads. In addition, because they're usually lighter than men, women tend to lift out of a seat in a rear end crash, which puts their heads in an even worse position.
The movement of the active head restraint seat actually seems to stop women from lifting so much, Viano said, and that allows the restraint to do its job.
As Olsen put it, "One of the practical benefits with Saab Active Head Restraint system is that it functions effectively even if not ideally adjusted. It suits the real world."
It also has significant benefits from a cost point of view, since it returns automatically to its passive position after deployment. "There are no pyrotechnics or electronics involved," Olsen pointed out, "and the system can be deployed repeatedly without any need for replacement or repair."
This contrasts sharply with the deployment of airbags, which require significant replacement cost at least.